Field of the Invention
The invention relates to a zero insertion force mount for fixing and making contact with circuit subassemblies on a substrate having a plurality of contact elements and a zero insertion force device.
In modular electronic systems with a variable configuration, a system circuit board with one or with a plurality of installation spaces (slots) is usually provided. The slots are respectively populated with a modular component, depending on the requirements on the system or on the level of expansion of the system, or remain unpopulated.
A typical example of such a modular system is a computer system (PC, workstation, server) with a working memory that can be expanded. Slots for memory modules are provided on the system circuit board in the form of insertion mounts and are populated with memory modules, depending on the desired size of the working memory.
Normal memory modules such as SIMMs (single in-line memory modules) and DIMMs (dual in-line memory modules) have contact surfaces disposed along a contact edge of the memory module, on one side or both sides, in order to make electrical contact. When the memory module is installed in the slot, the memory module is inserted with the contact edge into the insertion mount (edge connector). For this purpose, the insertion mount has, on inner sides of a holding device formed as a groove, contact elements that correspond to the contact surfaces of the memory modules and that, during population, are deformed and exert a spring force resulting from the deformation on a memory module inserted in the holding device.
The number of contact elements per insertion mount is 168 for memory configurations with SDRAM components (synchronous dynamic random access memory), 184 for memory configurations with DDRI components (double data rate I DRAM), and about 240 for those with DDRII components (double data rate II DRAM). In general, for faster concepts of memory configurations, an increasing number of contact elements is to be expected in the insertion mounts.
With each contact element, the expenditure of force needed for fixing and removing the memory modules increases. The stressing of the system circuit board when fitting the memory modules rises and, to the same extent, so does the probability of damage to sensitive structures on the system circuit board or to the contact elements of the insertion mount. Thus, normal insertion mounts for memory modules are nowadays specified for only about twenty-five (25) insertion cycles.
However, the contact force exerted by each contact element may not be reduced significantly because, as the contact force decreases, the reliability of making contact is reduced.
In particular for testing semiconductor devices, use is made of test sockets with ZIF mechanisms (Zero Insertion Force mechanisms), with which population of the test socket that in particular looks after the contact elements of the test socket is possible.
Such a test socket is illustrated schematically in cross section in FIG. 2. The test socket 11 is disposed on a substrate surface 30 of a substrate 3 and has a zero insertion force device 9. A semiconductor device 21′ is provided on a carrier 22 that has contact-making devices 13′. Each contact-making device 13′ is assigned a contact recess 14 in the test socket 11. The recess is bounded on one side by a section of a contact-making device 13.
The zero insertion force device 9 includes a lever arm 91 that can be rotated about an axis of rotation 94, a slide 95 that can move parallel to a substrate surface 30, and a conversion device 93. The conversion device 93 converts a rotation of the lever arm 91 into a displacement of the slide 95. The slide has a limiting element 12 for each contact recess 14.
In an unpopulated state of the test socket 11, in this case the limiting elements 12 are located on the side of the contact recesses 14 respectively located opposite the contact-making devices 13.
When the carrier 22 is fed into the test socket 11, the contact-making devices 13′ of the carrier 22 in the contact recesses 14 are in each case disposed between one of the contact-making devices 13 of the test socket 11 and one of the limiting elements 12 of the slide 95. As a result of rotation of the lever arm 91 in the counterclockwise direction, the slide 95 is moved to the left. In the process, the contact-making devices 13′ of the carrier 22 are clamped in between one of the contact-making devices 13 and one of the limiting elements 12 in each case. The carrier 22 is therefore connected mechanically and electrically to the substrate 3.
However, a test socket like the one illustrated in FIG. 2, however cannot make contact with DIMMs with rows of contact surfaces located on both sides, along a contact edge of the memory module. In this case, contact elements would have to be provided in the contact recesses of the test socket of FIG. 2 for both sides of the contact edge and connected to the substrate by fixed contact-making devices. However, the slide 95 would then no longer be movable.
A zero insertion force mount of a different kind for memory modules is disclosed by Jones et al. in U.S. Pat. No. 6,371,781. In this case, before the actual fitting of the memory modules to the slot, mechanical adapters having snap-in connectors are fixed to the memory modules: for example, by being screwed or riveted. When fitted at the slot, the snap-in connectors latch into prepared matching pieces of the zero insertion force mount. The snap-in connectors then press the contact elements onto the memory module in the fitted state. In this case, the insertion force needed for fitting is reduced by the wedge-shaped configuration of the snap-in connectors.
The disadvantage with such a zero insertion force mount is in particular the high expenditure and the high space requirement. The high space requirement is disadvantageous in particular in a configuration of a plurality of such insertion mounts beside one another because, with the distance of the slots from one another, propagation time differences of signals fed into memory modules provided in the insertion mounts also increase. It is precisely for future, fast systems that such zero insertion force mounts can be used only conditionally.